1. Field of the Invention
The present general inventive concept relates to a method and apparatus to encode and decode a speech signal using a code excited linear prediction (CELP) algorithm. More specifically, the present general inventive concept relates to a method and apparatus to search a fixed codebook by which a bit rate is reduced without degrading performance in an enhancement layer based on the CELP.
2. Description of the Related Art
Speech codecs employing a CELP algorithm are widely used in mobile communication systems and are based on linear prediction coding (LPC).
These speech codecs that use the CELP algorithm encode a speech signal into a core layer including encoding information that can restore a minimal quality of sound and an enhancement layer including additional bits other than bits provided by the core layer to enhance the quality of restored sound. Accordingly, these speech codecs decode the encoded speech signal.
The core layer and the enhancement layer typically share spaces of an identical fixed codebook. Due to the space sharing, a number of codes to be represented increases, so that a bit rate increases.